Hauraki Gulf research on snapper nurseries

Monday, 5 December 2016

Marine ecologist Mark Morrison wants to find where baby snapper hangout and how changes to the norrthern east coast environment affect these nurseries.

Snapper hot spots can be a closely guarded secret for keen fishers, but researchers are hoping they'll be more open about the areas they only seem to catch little ones.

For fish stocks in the Hauraki Gulf to stay healthy they need plenty of young fish growing on.

Young fish are attracted to certain 'nursery' areas for feeding and protection and this is all tied up with what's happening on the sea floor.

NIWA marine ecologist Dr Mark Morrison says they are particularly interested in populations of juvenile snapper less than 10cm long, in the Hauraki Gulf and East Northland, or small blue cod and tarakihi in the Marlborough Sounds.

Extensive mussel beds like off Great Barrier Island were once common in the Hauraki Gulf

For snapper in particular this includes sea grass meadows, horse mussel beds and sponge gardens.

* Crayfish 'functionally extinct' in the Hauraki Gulf

* Kaipara is 'last harbour standing'**

The sea floor has changed over the years and the researchers want to talk to people who have been fishing, diving or just living on the shore for a long time and can remember where the nurseries were before and if they have changed or moved. In particular from the shore out to about 30m deep.

Keeping track of nurseries hasn't been a big focus in the past but as management of fisheries and the Gulf becomes more ecosystem based, knowing more about the over all health of the Gulf is important.

Commercial dredging saw massive green mussel and horse mussel beds in the Gulf destroyed in a boom and bust industry that ended in the 1960's.

The beds which would have been an important habitat for young fish have never returned.

But with a massive catchment area, silt is also altering the seabed and smothering habitats young fish would have used in the past.

Along with interviewing people, the scientists are keen to have a look at historical records that may help in understanding the wider environmental history of the Hauraki Gulf/East Northland and Marlborough Sounds.

'Historical photographs, personal field diaries or fishing logs would be particularly valuable in helping to understand how things have changed,' Dr Morrison says.

'Our goal is to identify where and how habitats function, and work on increasing the survival rates of small fish. We will use surveys and experiments to learn how the habitats operate, where they are and what threatens their existence.'

A computer model will also be built to enable the researchers to explore 'what if' scenarios to help decide on the best management actions for the future.

A similar project was undertaken in the Kaipara Harbour a few years ago and gave a much greater understanding of it's current health. It also helped highlight the extensive damage silt flushing into the harbour off agricultural and forestry land was having, including on the last remaining nursery habitat of the west coast snapper fishery.

More info: www.niwa.co.nz/fishsurvey